Special Report 020

A Guide to Kimberlite-Indicator Mineral Trends in Alberta Including Observations from Recently Compiled Indicator Mineral Data

Since 1990, diamond exploration in Alberta has resulted in the discovery of 48 kimberlitic pipes and the recovery of more than 18 000 possible kimberlite-indicator minerals from surficial sampling (till, stream sediment and bedrock). The proper classification and interpretation of kimberlite-indicator mineral datasets are vital to the future discovery of kimberlites, and more importantly, diamonds in Alberta. Hence, the following review includes an updated guideline to kimberlite-indicator minerals being recovered, a synopsis of some of the important geographic and geochemical trends and their relevance to future diamond exploration in Alberta.

Of primary importance, the indicator mineral data include more than 1000 anomalous samples from across Alberta and make it clearly apparent that

- Alberta is under-explored. For example, few KIM surveys have been completed north of latitude 58°N; and

- there are other areas of northern Alberta (i.e., besides the known kimberlite areas) with high grain counts and excellent mantle xenocryst chemistry. These anomalous data and sample sites indicate that, with continued exploration, it is likely a significant number of kimberlites remain to be discovered both in the areas where kimberlites are known to currently exist and in areas currently with no known kimberlitic pipes.

Areas that display high potential for future kimberlite discovery includes, but is not limited to, the Buffalo Head Hills, Utikuma Lake, Calling Lake and St. Paul to Cold Lake areas. A number of other regions that have seen much less exploration, such as the Birch Mountains, Mountain Lake, Caribou Mountains, Chinchaga River, Peace River to Spirit River, Kakwa-Wapiti River, Edmonton and south-central foothills areas, and much of central to southern Alberta across the Prairies, require further exploration to identify the potential for kimberlite pipes and to determine the diamond potential based upon the chemistry of the associated indicator minerals.

The data also allow for geological interpretation regarding the mantle, particularly in identification of regional characteristics and similarities or differences in the mantle beneath Alberta. For instance, garnet and chromite in northern Alberta have significantly higher Cr versus garnet and chromite recovered from southern Alberta. This is believed to represent a major fundamental difference in the mantle between northern and southern Alberta. Furthermore, pyrope garnet from northern Alberta displays a noticeable trend of increasing TiO2 enrichment from west to east, reflecting a significant change in the composition of the upper mantle, possibly due to easterly increasing metasomatism. Finally, clusters of kimberlite-indicator minerals with unique geochemical assemblages must be related to mantle heterogeneity (e.g., Calling Lake area in northern Alberta). These observations reveal the complexity of the mantle underlying Alberta and the necessity for future kimberlite-indicator mineral sampling and compilations that will enable continued development of models required to assist in the discovery of an economic diamond deposit in Alberta.